The present invention relates to the release of pharmaceutically active compounds from biomaterials, including bulk materials and colloidal materials. Nucleophilic addition reactions are used for the conjugation of the pharamaceutically active compounds to the polymers to achieve the desirable release rates featured by the compositions of the invention.
Synthetic biomaterials, including polymeric hydrogels and water-soluble copolymers, can be used in a variety of applications, including pharmaceutical and surgical applications. They can be used, for example, to deliver therapeutic molecules to a subject, as adhesives or sealants, as tissue engineering and wound healing scaffolds, and as cell transplant devices.
The use of materials for the release of pharmaceutically active compounds has been studied by several groups. Pitt and Schindler categorized the various types of controlled drug delivery schemes (Pitt et al., Controlled Drug Delivery, CRC Press, Boca Raton, Fla., p. 53-80, 1983). They defined two types of systems in which the drug was covalently attached to a material. Systems in which the drug was pendently attached to the polymer were called Type IV systems, and systems in which the drug was incorporated into the polymer backbone were called Type V systems. This definition of Type V polymers was further expanded by Baker (Controlled Release of Biologically Active Agents, p. 84-13 John Wiley and Sons, New York, 1987) who included systems in which a free radical polymerizable group was added to a drug, with subsequent free radical polymerization of the drug alone or with other comonomers to form a material (for examples, see Duncan et al., Adv. In Polym. Sci. 57:51-101, 1984). Type IVb systems are different from Type V systems in that a linker molecule is utilized to connect a drug to an active group on a polymer.
While much progress has been made in the field of polymeric biomaterials, further developments must be made in order for such biomaterials to be used optimally in the body. For the release of a therapeutic compound from a biomaterial over a clinically relevant time-frame, the half-life of the release of the therapeutic compound from the biomaterial should be on the order of weeks or months, rather than on the order of hours or years, as has been the case when biomaterials are placed under physiological conditions. In fact, the clinical usefulness of the delivery of pharmaceutically active compounds from biomaterials has been limited due to the lack of control of the rate of release of pharmaceutically active compounds from the biomaterial and the great difficulty and low yields associated with the conjugation of these compounds to the polymer.